The present invention relates generally to a seat belt retractor assembly incorporated in an automobile or other vehicle for securing the occupant(s) and, more particularly, to a seat belt retractor that locks the reel shaft, which winds the webbing on it in the event of an emergency, against rotation, thereby preventing the webbing from being unwound.
A conventional seat belt retractor incorporated in an automobile or other vehicle is provided with lock means for locking a reel shaft, which winds a webbing on it, against rotation in the event of an emergency such as when the car is excessively decelerated, thereby preventing the webbing from being unwound due to the inertial motion of the occupant.
One typical example of the lock means for such a reel shaft is set forth and illustrated in the specification and drawings of U.S. Pat. No. 4,796,918. This is called a frame lock type of lock means, including a reel shaft and teeth provided on a frame that supports the reel shaft. Upon deceleration larger than a predetermined value applied to a vehicle, the reel shaft is moved until its teeth mesh with the teeth of the frame, thereby locking the reel shaft against further rotation. This frame lock type of lock means can be relatively reduced in weight, because it is possible to dispense with any special member because of forming teeth on the frame. Accordingly, this lock means may well accommodate to weight reductions which current vehicles such as automobiles must achieve.
As mentioned above, further unreeling of the webbing may be avoided by locking the reel shaft against further rotation upon excessive deceleration applied to a vehicle. In some cases, however, excessive webbing wound on the reel shaft is tightly wound up by unwinding force on the webbing, and this tight winding-up tends to unreel the webbing further.
As disclosed in JP-A-03-112750, there is thus proposed another seat belt retractor that is designed to lock a reel shaft against rotation and clamping a webbing by clamp means to lock up the webbing, thereby preventing the webbing from being further unreeled.
In the seat belt retractor disclosed in this publication, a pawl is engaged with teeth of a ratchet wheel formed on the reel shaft, thereby locking the reel shaft against rotation, and some operable member is used to actuate the clamp means in operable association with the motion of this pawl, thereby locking up the webbing.
In a retractor including such lock means as disclosed in the specification and drawings of the above U.S. patent, the teeth formed on the reel shaft mesh with the teeth of the frame. Therefore, when the reel shaft is locked against rotation, relatively large forces are applied to the teeth of the reel shaft and the teeth of the frame. It is thus required to increase the widths of these teeth so as to relieve stress exerted thereon. So far, the stress exerted on the teeth has been relieved by increasing the thicknesses of the teeth of the reel shaft and the frame, thereby increasing the width of engagement, or by forming separate teeth on the frame for reinforcement. However, a weight-increase problem arises in the former case. In the latter case, not only are more parts needed because some reinforcement must be used, but more steps are needed because of an additional step of reinforcement attachment, thus incurring some considerable expense.
In the case of the frame lock type of lock means mentioned above, it is required that the teeth formed at both ends of the reel shaft mesh simultaneously with the teeth formed on both sides of the frame. However, some considerable difficulty is indeed experienced in achieving simultaneous engagement on both sides; such engagement often takes place on one side. It is particularly difficult to achieve simultaneous engagement on both sides, because the reel shaft is moved to engage the teeth on the reel shaft side with the teeth on the frame side. Where the teeth are engaged with each other on one side alone, stress concentrates on those teeth, resulting in need of further strength increases, and this leads inevitably to size and weight increases in retractors.
In order to prevent the webbing from being unreeled due to its tight winding-up, it is desired to incorporate such webbing clamp means as disclosed in JP-A-03-112750 in such a frame lock type of seat belt retractor.
However, it is difficult to apply the clamp means disclosed in this publication, without any modification thereto, to the above-mentioned frame lock type of seat belt retractor that is designed to move the reel shaft until the teeth on the reel shaft side mesh with the teeth on the frame side. This is because this clamp means is actuated by engaging the engaging claw of the second operable member with the teeth of the ratchet wheel formed on the reel shaft to transmit the rotational force of the ratchet wheel from the second operable member to the clamp means through the first operable member.
This clamp means is much more complicated in structure due to using a much more increased number of parts and combining such parts. This is because it must be constructed from the pawl for locking up the reel shaft, the second operable member for taking the rotational force of the reel shaft, the first operable member for transmitting such rotational force from the second operable member to the clamp means, and the operable member for associating the motion of the pawl with the motion of the second operable member.